Procedure for the preparation of prostheses of great strength from methyl methacrylate monomer and polymer



fiatenteci Feb. 14, l fi UNITED 1 STATES PATENT. OFFICE -PROC'EDU'RE FOR THE PREPARATION, OF PROSTHESES OF GREAT STRENGTH FROM METHYL MErHAoRYLarE MONOMER AND POLYMER Max- Ilaefe'li, Basel, Switzerland 1 Claim. (Cl. 18-551) i There have been known various processes for example, from polyvinyl-, polystyrene-, polyacryl-resins, or from condensates, for example, phenol-formaldehyde resins. In this process, the

. finished polymerized products or pre condem sates in a heated plastic condition were filled or injected into the mold and hardened, if necessary, or otherwise the compounds not yet polymerized, for example, monomeric vinyland methacrylio ester, styrenes, etc., in liquid or, if necessary, in sirupy state due to partial polymerization, are filled into the mold and converted into solid bodies by polymerization with the application of heat.

Other processes reside in methods using polymerisates inp'owder-granular form in combination with liquid, monomeric compounds capable of being polymerized. According to this method, granular polymerisates are mixed withthe monomeric liquid in such a manner that either the polymers swell, so that they will no longer settle out in the mixture (stirring the monomer and a granular polymer together only as long as is necessary to thoroughly wet the individual granules and bring about suificie'rit swelling, so that the granules have little or no tendency to settle out). Also, the mixture of monomers and polymers may be stirred and kneaded in such a manner or left standing for such a period, for example, 8 to 14 days, that a mass of a soft, viscous,

plastic or rubber-like consistency is obtained,

plastic kneadable or soft rubbery consistency. The masses thus treated are then filled into the mold and solidified therein. These processes are broadly based upon the theory that in the preparation of molded bodies, it is necessary to thoroughly mix the monomers and polymers with one another and treat them in such a manner that the polymers are swelled by the monomers or that the two substances are mixed together 2 necessary on the one hand to use polymerisates which themselves are highly polymerized and soluble with difficulties. On the other hand, these polymerisates are to be mixed slightly with the monomeric liquid for a short period of half a minute at maximum, for example, for 10 M seconds. As a result of said slight mixing action of half a minute at maximum, the mentioned high-molecular polymerisates which are soluble with difficulties, are merely wetted with the monomeric liquid, so that the individual grains cannot swell nor can a plasticmass be formed. The mixture constitutes a moist, loose, and still granular mass, which is filled into the mold in this condition. High. polymeric polymerisates soluble with difficulties are not suited for the known methods, because these polymerisates are swelled by the monomers onlyslowly or yield said monomers for a longer period, said masses being very viscous and hardly adapted to be treated (worked up) for dental purposes.

- In the process according to .the invention, prostheses can be made, which have a homogeneous structure and possess great strength, as it has been ascertained bymeans of microscopic examinations and strength tests.

A further advantage of the present invention consists therein that only a small amount of monomerous liquid is required to moisten the powder as, generally speaking,'1 weight-part of liquid is used for 3 weight-parts of powder. After having gained some experience in this respect, even smaller quantities of liquid may be used, for instance, 1 weight-part of liquid to 4-5 weight-parts of powder, particularly when operating with heated forms. when producing caoutchouc-like, pasty intermediate masses, fairly substantial quantities of monomerous liquids, or of low molecular polymerised products are required, in order to obtain the requisite plasticity. The more liquid that is employed, the more diiiicult it is, due to the shrinkage of polymerisation taking place, to produce formed bodies, in accordance with the measurements required, and to keep these bodies On the other hand, i

to the temperature at which complete hardening takes place. This can be done, for instance, by placing the filled form into cold water, heating it up to the temperature of polymerisation, and by further heating for some time.

Eidmple For the preparation of a dental prosthesis,

monomerous methylmethacryl-ester, to the extent of about /3 of its weight-amount, is poured over z a highly polymerised, difliciiltlysoluble, bi'g-surfaced methylmethacrylate powder in a deep vessel, and subjected to a short mixing-process, i. e. to /2 minute, and homogeneouslymois'tenedby means of a spatula, or a glass rod. The-homogeneous wetting is recognized by thehomo'geneous colour of the powder. The moistened porous powder is put into the lower half of the vessel,

and formed in the well known manner. "is,

forinstance, effected i'nthe following way: The

eistened powderisfdistribiited in S'u'cha manner p the vessel that"the greatest accumulation of v ater'ial takes place at the thickest parts' of the prds thesis to be prepared. "Subsequently, the .yes's'el, 'by the use of an intermediate "viscose-foil (Qe11ux, Cellophane), can be closedgby slowly t lpcrees'mg the pressure, up "to millimetre. The vessel is re-opened, and the viscose-foil is taken wa By pressure ofthe moistened powo'er;anoniogeneousm'ss must have been'fo'rr'ned;

A'pulverulent state shows the insuflicient presence for material whereas excess of material should lbe removed. I Subsequent to this control, the vesseli's completely closed under the press, and 1 provided with atight hoop. The vessel mounted in this hoo'pis placedjinto aboili'ng-pot with cold "water, which is heated immediately, As soon as the boiling-point is'attained, 'the vessel isleft for half-an-hour in the boiling water. 'The polymerisation land the forming has how been accomplished, and after subsequent cooling, the prosthesis'may be 'takenout, 'andw'o'rk'edup.

Prostheses' of every description can be prepared l bythe above mentioned procedure. 'Aecording toflthefdemands and the use required, *the most eohvment initial products" will be sele cfied, for instance, high "fio'lymeris'ed 'vinyl-, a'cryl-, and iiithadryl-Ysihs; or miifd p'olymerised products,

.moloeica urpos s.

4 also hardened phenol-formaldehyde-, or glyptalresins, which are moistened by corresponding, suitable compounds, capable of polymerisation or condensation, for instance, vinylchloride, vinylacetate, solutions of,'hexamethylene-tetr-amine af'cidjin 'pul'verii'l'ent rpm, the" grainsranging in "size froin' fiiie to fco'ars'e'with 15 to 25% 'Of a. monoifierimmethyl "ester of methacrylic acid in '"su'ch'a 'WayQth'a't'the polymers do not swell and the mixture forms a moist, loose, granular mass,

"filling" a mouldimmediately with'saidmass, heating' said mould "with the massfand compressing said massin "said mould untilsaid massis hard- *REFERENGES "CITED iThelfollowing references are of record in the file of this patent:

UNITED STATES PATENTS Numben Name I Date 2,028,776 ,Hibbert :Jan. 28, 1936 12,335,993 Vernon 'et a1. Mar. 18, 1 941 ;2,z9'1,24s Rudolph Sept. 29, 1942 73,335,371 Willis Nov.' 30, 1943 2,347,320 Hilt'n er Apr. 25, 1944 FOREIGN PATENTS ti e: ,itbi ri v I 4 343 fi ea fi e '--lM 1. 3 

